A variety of hydrophilic polymers which are useful in the manufacture of water absorbent films and fibers have been reported in the prior art. U.S. Pat. No. 3,915,921 discloses copolymers of unsaturated carboxylic acid monomers with alkyl acrylate esters wherein the alkyl group contains 10 to 30 carbon atoms. However, because of the high Tg of these polymeric materials, it is difficult to extrude them in fiber or film form. Furthermore, films pressed from the powders require high temperatures, the films are brittle and fragile, and have a reduced initial rate of water absorption.
U.S. Pat. No. 4,062,817 discloses polymers of unsaturated copolymerizable carboxylic acids, at least one alkyl acrylate or methacrylate wherein the alkyl group has 10 to 30 carbon atoms and another alkyl acrylate or methacrylate wherein the alkyl group has 1 to 8 carbons. This composition alleviated many of the deficiencies of the earlier compositions. Further improvements in the hydrophilic properties were obtained by compositions disclosed in U.S. Pat. No. 4,066,583. This patent discloses a composition comprising (1) a copolymer of the type disclosed in the '817 patent, except that after copolymerization 30 to 90 percent of the carboxylic groups were neutralized with an alkali metal or ammonia and (2) an aliphatic glycol, a plasticizer which is important in facilitating extrusion of the polymer.
Most recently, U.S. Pat. No. 4,167,464 discloses highly water absorbent polymers obtained by photopolymerizing an alkaline metal salt of acrylic acid, a long chain alkyl acrylate or methacrylate, and a short chain alkyl acrylate or methacrylate in the presence of a photoinitiator.